Originally Posted by JAJ

So the bottom line is that if your next child is born in the UK he or she will automatically be British, however if it's born outside the UK then you'll have to jump through some registration hoops pretty quickly (or move back to Britain later).

A lot of people miss these time limits, either because they don't get around to it or they think their child is British when it is not.

As far as the U.S. is concerned, your child is an American citizen, you may want to think about the pros and cons of becoming a U.S. citizen yourself before leaving the States. It is something you may find useful later on, eg if your child wants to live in the U.S. as an adult and you want to join him (or just spend extended visits, longer than the 3 months you get on the visa waiver). There are also tax issues (both positive and negative) to consider.